Sheol

Sheol (pronounced "shee-ohl") is a level that was added in the Halloween Update. The walls appear to be the same material found in the Devil Room, most likely a reference to the name of the level, meaning "underworld" in Hebrew. Unlike other chapters, Sheol only has one floor, with Satan as the boss.

Like in The Womb, many rooms contain past bosses, but now the bosses are also drawn from The Depths and Womb, as well as Harbingers. Like in The Womb, there are even duplicate bosses, although they are more common now (Especially Loki and Gemini).
In addition to duplicates of Sins, Sins accompained by other enemies, or even duplicates of Sins with other enemies, are common.

Challenge Rooms are the only unique rooms in Sheol. They usually consist of three boss fights in a row, but can give the same monster spawn patterns as The Womb[1].

Sheol can be accessed early if a Devil/Angel room spawns after killing Mom's Heart. You will unlock both the ending and the appropriate item when you enter the devil room. By ending the boss fight with full health, this chance is increased substantially, though a devil room is not guaranteed. Sheol can also be accessed through the Angel Room, by using We Need To Go Deeper!, using the joker card or teleporting to the Error Room from Womb 2, regardless of whether Mom's Heart has been killed before. After defeating It Lives for the first time, access to Sheol is guaranteed for future games.

Walks towards Isaac, dealing one heart of contact damage. Turns into a pile of goo after taking enough damage, where it can be killed. Will regenerate after a short amount of time if not killed quickly.

Two joined twins that compose 50% of the health bar each. The large twin runs towards Isaac, while the smaller twin fires fast-moving blood shots. The smaller twin will stop firing blood shots upon the larger twin's death, and instead start chasing Isaac.

Charges out of the room, returning to his previous spot where he started the charge. Spawns Pooters when Isaac is not in his line of sight, up to a maximum of 2. Upon reaching 33% of his health, he will lose his lower body and no longer charge at Isaac. Instead, he fires 3 fast-moving blood shots at Isaac in a single spot, with a small delay.

Charges to the left or right of the room, returning close to his previous spot upon charging 3 times. Fires 8 fast-moving blood shots in all directions. Occasionally goes to the top of the room, becoming invulnerable and spawning multiple Troll Bombs

Upon reaching 50% of his health, he will lose his horse and instead start walking towards Isaac at high speeds, dealing contact damage. During this phase, he can sometimes stop and drop to the ground, making him more vulnerable to damage.

Spawns four scythes in random areas of the room, making them whirl towards Isaac.

Upon reaching 50% of his health, he dismounts his horse, which starts charging around the room in a pattern similar to War. The horse can now be destroyed, but it will not damage Death's health bar. Death himself will start spawning Knights